Pages

Friday, January 8, 2010

Mommy Dearest

It was a dark summer night, I was up to my knees in a southwestern Georgia pond, and I just saw the scariest thing I could imagine. I was there trying to figure out how much effort was needed to catch a large sample of water snakes for a future study and my eyes were focused on keying into their serpentine shapes along the shoreline. But when I caught sight of a large mound of sticks and dirt just above the water’s edge, that’s when I started to get nervous. I slowly and instinctively turned and looked out across the center of the open pond and, just as I had suspected, the light from my headlamp reflected back at me from dozens of little yellow eyes. I had stumbled across an alligator nest and the small pond was covered in recently hatched animals. It wasn’t these baby alligators I was afraid of though, it was the mother, assuredly somewhere close, watching my every movement. And mother alligators are very protective.When a female alligator feels her time is near, she’ll laboriously construct a mound of mud and debris and lay her eggs in the middle of it. After carefully covering up the eggs with more mud and plants, she’ll retreat to the nearby water and wait. If a raccoon or other potential egg predator ventures too close, she’ll torpedo from the water hissing with mouth agape. It’s an intimidating display, and an effective one. But her motherly duties don’t stop there.When the baby alligators hatch in late August, they begin to emit a guttural chirping noise. These chirps alert the mother alligator of the new arrivals and she starts to excavate them from the nest. After uncovering the youngsters, she’ll delicately pick them up in her mouth and carry them to the nearby water. The babies will stay with the mother for up to a year and their chirps, which they’ll utter when distressed, continue to inspire a prompt protective response from the dedicated parent. Alligators make excellent parents (at least the females do), and that makes them unique among reptiles. Take turtles for example, females will lay their eggs in a nest some distance from the water, cover them up, and then never have anything to do with her young again. Most reptiles will lay their eggs (or in the case of some groups, give live birth), and let them fend for themselves. One interesting exception includes some pythons; females will coil themselves around their clutch of eggs and shiver to generate warmth.But when it comes to protecting the young after they’ve hatched or been born, alligators are apparently a reptilian exception. They’re the only ones seeming to demonstrate bona fide parental care, parental care being the term used in scientific circles. What is parental care anyway? Mammals nurse their young, birds bring food back to the nest for their young; alligators don’t do anything like that at all. But, would anybody doubt that chasing away potential predators from their babies is taking care of them? It’s probably best to consider parental care as any behavior that increases the chance of survival among offspring.What’s more, it’s probably safe to say this behavior is due to a genetic attribute, at least in alligators. Alligators that are good mothers give birth to young that carry this same genetic disposition, those young have a good chance of surviving to adulthood because they’re taken care of, and these young can then breed themselves and take care of their young, and so on. If we don’t think that parental care is due to an animal’s genes, what alternative is there? That alligators learn to take care of their young? That seems to be an unlikely scenario. If we accept that behavior can be influenced by an individual’s genes, it’s easy to see how a beneficial behavior like parental care can evolve.So, to include alligators among the group of animals that exhibit parental care, we must broadly define parental care as simply any behavior that increases the survival of young. And if we do this, we may need to reexamine the other reptiles we previously dismissed. For example, let’s take a look at the turtle we mentioned earlier, the turtle that just lays her eggs and leaves. If some females have a genetic predisposition to build their nests in areas where predators are unlikely to find them, such as under dense vegetation, does that count as parental care? It might.Another interesting example includes the rattlesnakes we have in the region. Many naturalists have observed female rattlesnakes that have recently given birth surrounded by their new babies. These snakes may be found together for some period of time, crawling over each other in their refuge, usually some sort of underground shelter. Is the female sticking around because the babies are safer when she’s there? Or maybe the birthing process was so exhausting that she needs a few days to recuperate enough energy to leave. It might not matter in this case, in both scenarios the end result is the increased survivorship of the young, therefore, it’s parental care! Even if it does sometimes backfire.

These thoughts weren’t of much concern to me as I wading through the water that dark summer night. I managed to make it back to dry land without pissing off the mother alligator; I even found and caught a few water snakes while simultaneously keeping one eye peeled for any sign of an impending attack. I decided though, I could find different wetlands for further study. Alligator photos courtesy of Matt Greene.Photograph of yours truly courtesy of Sean Sterrett.